A comparison of high speed differential scanning calorimetry (Hyper-DSC) and modulated differential scanning calorimetry to detect the glass transition of polyvinylpyrrolidone: the effect of water content and detection sensitivity in powder mixtures (a model formulation)

Abstract

Differential scanning calorimetry is an established technique for the measurement of glass transition temperature (Tg). More recently modulated DSC has been used, a technique that allows the separation of the reversible Tg response from non-reversible events, allowing a more straightforward detection of glass transitions. However, even when using modulated DSC, the sensitivity is such that detecting glass transitions of amorphous components can be a challenge, particularly when the amorphous form is present at low levels. With Hyper-DSC the sample is ramped at a very fast scan-rate (up to 500°C/min). The rapid scan-rate can substantially enhance the sensitivity allowing small transitions to be detected more readily. The purpose of this study was to determine how much of an increase in sensitivity could be achieved whilst checking how results may be affected by the high scan rate. The Tg of PVP at various moisture contents was measured using both modulated and Hyper DSC. A comparison of the results demonstrated that the temperature of the Tg measured at the high scan rate was not significantly different from the temperature of the Tg obtained by modulated DSC. Also results for both techniques compared favourably with theoretical values calculated using the Gordon-Taylor equation. Additionally the size of the Tg was significantly larger when measured using Hyper-DSC. The increase in sensitivity was further demonstrated by measuring the Tg of PVP in a series of mixtures of PVP and lactose ranging from 5 up to 50% w/w PVP. Modulated DSC was only able to detect levels of 40% w/w PVP and above whereas Hyper-DSC was easily able to detect the Tg of PVP in all samples.